Display technology used in many television and computer applications typically uses a backlight panel or plate for illumination of a display, particularly a liquid crystal display (LCD). For example, LCD displays are commonly used in such exemplary applications as notebook computer displays, computer monitors, wireless cell phones, and flat-panel televisions. The display backlight generally includes a planar light guide configured to spread light from a light source located at an edge or edges of the light guide across the surface of the display.
FIG. 1 depicts a conventional display backlight arrangement including a cold-cathode compact fluorescent light (CCFL) source. As shown in FIG. 1, the light produced by the CCFL propagates into the edges of the light guide. The light is internally reflected until it reaches the reflective surface on the bottom of the light guide. After striking the reflective surface, some of the light reflects up and out of the light guide. However, not all of the light that enters the light guide from the edges is emitted uniformly from the light guide surface that is opposite the reflector.
As such, conventional CCFL display backlight assemblies, such as the one shown in FIG. 1, are limited by a number of drawbacks. For example, these assemblies are typically fragile and contain environmentally hazardous material, such as mercury. Furthermore, conventional CCFL display backlight assemblies fail to produce a full spectrum of light. In addition, the assemblies cannot be rapidly switched to reduce frame jitter.
Disadvantageously, many typical display backlight assemblies include a physical gap between the CCFL and the light guide. Generally, the physical gap is maintained between the two elements because the fluorescent tubes are very thin and fragile (e.g., a 19-inch LCD display includes tubes that are approximately ⅛ of an inch in diameter), and highly susceptible to damage if placed in physical contact with the light guide. Due to the physical gap, however, the emitted light is not efficiently coupled from the CCFL into the light guide.
Like the example shown in FIG. 1, many conventional display backlight assemblies are edge lit, meaning that the fluorescent tubes are arranged at the edge of the light guide, as opposed to behind the light guide. By positioning the tubes along the edges of the light guide, a thinner display may be produced. However, displays that are edge lit by fluorescent tubes do not project a large range of quality light, thereby limiting the overall size of the display that may be produced using an edge-lit arrangement.
Finally, in general, conventional compact fluorescent light provides a poor color rendition, particularly with respect to the color red and the like. Thin-film transistor (TFT) LCDs have been developed to address the poor color rendition provided by compact fluorescent tubes. These LCDs typically include one or more TFT filters designed to take the white light produced by the CCFL and filter it into red, green, and blue pixels. Next, the TFT corresponding to each of those pixels turns on, off, or partially on to create a single pixel consisting of a combination of the three colors. However, as much as 75% or more of the white light emitted by the CCFL may be lost in the TFT filters.
Accordingly, there is a need in the art for a display backlight assembly that provides improved coupling and color mixing using an edge-lit arrangement.